The invention relates to a method of producing microsensors with integrated signal processing wherein the electronic circuits for the signal processing and the sensor structures coupled therewith are produced on a common substrate immediately adjacent one another in space.
It is known to produce microsensors of this type by combining methods of semiconductor technology and the anisotropic silicon etching technology so as to produce on a silicon wafer in one process sequence the electronic circuits and the sensor structures coupled therewith. Such a manner of proceeding for the production of a capacitive acceleration sensor is described and illustrated by K. E. Petersen, A. Shartel and N. F. Raley, in "Micromechanical Accelerometer Integrated with MOS Detection Circuitry," IEEE Transactions on Electron Devices, Vol. ED-29, No. 1, January, 1982, pages 23 to 27. According to FIG. 1 of that publication, a structured p-doped layer is initially produced in the surface of an Si wafer as the electrode and etch stop layer. Then silicon is precipitated epitaxially to a thickness corresponding to the spacing of the electrodes and a structured silicon oxide layer is produced. By means of anisotropic etching, a contact hole is made through the opening in the silicon oxide layer, through the epitaxial silicon layer, down to the buried electrode. The source and drain regions and the electrical connection in the contact hole are produced by doping. Then the gate oxide is produced and an etching window is opened in the silicon oxide layer for the later formation of the sensor structure in the form of a reed. Then, the electrical connections are made and the reed region is metallized. As the last step, anisotropic silicon etching forms a trough between the buried electrode and the silicon oxide, thus creating a metallized silicon oxide reed which is able to vibrate.
The drawback of this processing sequence is that standard semiconductor processes such as, for example, oxidizing and doping, are employed in alternating succession with anisotropic silicon etching processes. This leads to problems in mass production since the use of alkali etching agents in the anisotropic etching process involves the danger of undesirable changes in the characteristics of the electronic circuits.